There are many different types of disc dispensers available for dispensing sensitivity discs in a predetermined pattern onto the surface of a culture medium within a receiving dish. Certain types of structures are designed for dispensing a single disc at a time from a single cartridge and others dispense, for example, 8 to 12 discs in a predetermined pattern. With the multi-disc dispensers there are separate disc containing cartridges for each position on the dispenser.
Certain types are rotational dispensing mechanisms where one portion of the dispenser rotates with respect to another portion in order to dispense the discs. Others rely on a reciprocal vertical plunger type of arrangement which employs linkage to dispense a disc from each of the cartridges in the dispenser. In the majority of dispensers which have been used throughout the years, once the dispensers have moved a disc from a cartridge into alignment with a discharge port the disc is permitted to fall freely onto the culture medium. Whatever control is maintained over the disc in its free fall is determined by the diameter of the opening of the discharge port and the length of the surrounding port through which the disc freely falls. Another factor which determines control over the freely falling disc is the height of the bottom open end of the discharge port from the culture medium within the receiving dish.
Examples of dispensers which utilize the freely falling dispensing mechanism when dispensing a plurality of discs simultaneously in a predetermined pattern are disclosed in U.S. Pat. No. 3,394,846 to Carski et al. and U.S. Pat. No. 3,300,087 to Kuypers. Various different approaches from the free fall method of dispensing have been attempted, one of which is the system employed in the Darpentigny et al. U.S. Pat. No. 3,836,047.
The object of all disc dispensers is to be able to provide a selected number of discs in an accurate predetermined pattern for a particular receiving dish and test to be accomplished. The device should be reliable and versatile. It is important that the discs intended to be dispensed on a particular stroke be all dispensed in an accurate and quick and efficient manner as possible. The dispenser is of the type which is reliable in the sense that repeated use will result in the same accurate and complete dispensing of the desired number and pattern of discs. Naturally, cost is also significant and in this respect simplicity of structure is desirable as well as low cost in materials. It should be kept in mind that a simplified structure increases the reliability particularly when dealing with a low cost mass produced device. Different types of antibiotic tests require a different number and arrangement of discs and virtually all tests depend upon accuracy in placement upon the culture medium.
Commonly assigned pending application Ser. No. 628,077 filed Nov. 3, 1975 now U.S. Pat. No. 4,042,145 and entitled Sensitivity Disc Dispenser With Tamper Mechanism represents a recent development in the state of the art relating to sensitivity disc dispensers and particularly in regard to the objects discussed above. The present invention incorporated the basic structure disclosed in that application and adds additional features which represent improvements in the art.